polarimetry

Grant,I'm glad to see that you are reviewing the literature. Kemp's 1986 paper (http://adsabs.harvard.edu/abs/1986ApJ...300L..11K) and the follow-up thesis by Gary Henson in 1989 (http://adsabs.harvard.edu/abs/1989PhDT........11H) really provided the analysis needed to show that the disk does not exactly bisect the star and that it is tilted (i.e. rotated) by about 5 degrees (North of East). Eps shows some particularly difficult polarization readings which Henson attempted to dissect in his Ph.D. thesis. He concluded that Eps (the primary) is a non-radial pulsator, but he was unable to tie down what, if any, pulsation modes were dominant.As for your question: the presence of any material around a star, called circumstellar material, definitely has an effect on the polarization of light. To make matters worse, the material between the star and Earth also causes polarization. In Kemp's paper he notes that the interstellar medium, or ISM, causes a 2% net polarization in his data. Under normal circumstances, a nearby (in space) star that is thought to exhibit no polarization would be used as a "calibrator" star so that the interstellar polarization (ISP) can be removed, but no suitable star was found in the vicinity. This leaves an approximate 2% net polarization in the data.Non-spherical particles are actually a strong cause of polarization. Several people are studying dust around stars using polarization data and IR observations. If the particles orientate themselves in a particular way, it can be detected. Modern instruments are capable of detecting polarization to less than 0.02%. Often the polarization around an object is quite minimal, being less than 1%, but every little bit of information helps us determine what is going on.I actually spoke for a few minutes about polarimetery during my talk at the August Adler meeting and specifically referenced the works by Kemp and Henson. When the video is posted online, it might be worth watching.-Brian

Thanks for the Kemp reference Brian, The proposed model with the disc tilted about the axis along our line of sight is interesting as I think it could explain the difference between ingress and egress in the KI 7699 line intensity seen by Lambert and Sawyer through the last eclipse which I mentioned in a separate thread. http://www.citizensky.org/forum/rotation-eclipsing-object Fig 2 in Kemp's paper implies that the full extent of the leading edge of the extended semitransparent region might not be seen, as the outer edge of it may not pass in front of the star. On egress, however the full extent of this region would be seen at the trailing edge. Cheers Robin edited to remove reference to asymmetry in radial velocity -most likelydue tochange in secondary RV from ingress to egress due to the orbit.